It is proposed to determine whether all taste fibers that respond predominantly to sweet substances are identical in their response to various sweeteners or whether the population is heterogenous. The study of the response of the population of taste nerve fibers as well as single nerve fibers will be utilized to determine the responsiveness of four different species of animals. Two-bottle preference studies will complement the electrophysiological studies. Since animals respond to a wide variety of molecular structures which are sweet to man, it is imperative to know whether we are dealing with a uniform population of receptor sites.